Refractive eye surgery relates to a change of refractive properties of the eye, e.g., by remodeling the cornea as one of the optical components of the eye. As an example, LASIK applies ultraviolet laser light for the remodeling. The present disclosure can be applied to the LASIK technique as well as the PRK and EPI-LASIK technique.
The cornea is remodeled according to an ablation profile, which is a 3-dimensional sub-volume of the cornea that is to be removed. A sequence of laser pulses interacts with the stroma of the cornea to ablate living tissue in a precise manner. In controlling the laser light acting on the cornea, a center of ablation is a crucial reference point. The sequence of laser pulses is applied relative to the ablation center. Existing systems for refractive surgery center the ablation profile to the pupil center. This is true for systems, which may perform a treatment of myopia, hyperopia, or astigmatism without import of diagnostic data, e.g., topographic data or wavefront data. However, the pupil center can shift relative to the cornea as the iris of the eye astringe or dilates. Techniques for compensating such a pupil center shift are described in European Patent EP 1 985 269 B1.
Some known systems allow for manually changing the ablation center away from the pupil center. For example, a surgeon can manually aim at centering the ablation profile on a visual axis of the eye. Such a centering offside the pupil center can be essential for patients exhibiting a high deviation between the pupil center and the visual axis, which typically includes cases of hyperopic eyes. However, the manual shifting of the ablation center away from the pupil center is based on a subjective visual estimate of the surgeon as well as the limitation of the instruments, e.g., the microscope resolution, arrangement and alignment. Also, the mere fact that the change is performed manually can imply uncertainty or add to an inaccuracy of the ablation result. Further, the manual shift is time consuming and requires additional effort by the surgeon.